ARM: dts: imx6-sr-som: add ethernet PHY configuration

Add ethernet PHY configuration ahead of removing the quirk that
configures the clocking mode for the PHY.  The RGMII delay is
already set correctly.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>